This invention pertains to the field of digital signal compression and quantification. More specifically, the present invention related to a method for optimizing signal quantification, particularly the quantification of signals transmitting still and motion image components.
Multiband compression methods have generally divided a signal into frequency components and then used some method to quantify the values in each of the frequency bands in order to represent the desired signal quality. Some of the problems with this approach include:
1. Only a small number of frequency bands are used so the regional quantification method is a less than optimal coarse approximation of the desired function.
2. Unequal quantification of neighboring frequency bands generally increases the amount of aliasing in the reconstruction mechanism.
3. Many quantification methods can generate undesirable artifacts in various degenerate cases.
4. Quantification as a separate process adds time or hardware to the implementation.
5. Quantification as a separate process can add additional noise.
What is needed is a system and method for quantifying one or more signals in an image stream such that the method can be easily implemented while offering better coding efficiency and more degrees of freedom in designing subband filters.
Wavelet compression of images generally consists of subband transforms of an image into frequency regions. These regions are then quantified to relative resolutions and entropy coded. The present invention uses a continuous and frequency specific function to quantify the regions rather than a regional approximation.
More specifically, the method uses reversible filters before and after signal quantification as a continuous function of the frequency domain. This allows the scaling function to be either the exact desired function, or more closely approximate the desired continuous quantification function. It also allows the characteristics of any quantification and aliasing artifacts to be tailored to the particular application. As a result, the present invention provides better interpolation of quantification errors resulting in less noticeable artifacts in the quantified stream. The present invention also provides lower aliasing energy between subbands.